On common knowledge
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There’s a funny thing about ‘common sense’ and ‘common knowledge’. We often use them interchangeably but they’re not quite the same.
Common sense is that supposedly self-evident wisdom you can appeal to when you don’t want to argue: ‘it’s just common sense.’ Politicians love it. So do op-ed writers. The problem is that common sense is subjective - and, as The New Yorker puts it, easily weaponised to dress up one person's nonsense as obvious truth.
Common knowledge is different and more interesting. In game theory, it means everyone knows something but also that everyone knows that everyone knows.
Take the Emperor’s New Clothes fable. When the child points out that the Emperor is naked, he’s pointing out something the crowds already know but he’s also letting everyone know that everyone else knows.
That recursive loop is what turns private belief into public certainty. As The New Scientist explains, common knowledge is the glue of so…
